Video Standards


Although the BetaMax/VHS standard war is long over, there
are a confusing number of different systems to choose from.
The standard you use will depend on the equipment you have,
and what you can afford.

Remember also that not all video standards are compatible.
For example, an SVHS system will not work properly with
equipment which uses VHS. To get the most out of your chosen
standard, all the equipment you use (players, recorders,
genlocks) must work with the same standard.


VHS

The first home video system, and quite poor by today's
standards. The tapes are large and bulky, and the vertical
image resolution is a paltry 240 lines. It suffers from poor
frame rate accuracy and crosstalk (black and white lines
close together will cause coloured bands to appear).

VHS-C

The smaller cassettes used in some camcorders are called
VHS-C. They can be used in special adaptor cassettes to
allow replay in normal home "full sized" players. The
picture quality is fine for home use, but still far from
professional quality.

VHS-HQ

A slightly improved version of VHS. Modern systems are of
this type, which is slightly better than standard VHS.


8mm

The very small tapes used in some camcorders are of the 8mm
system. The tape is a metal compound which gives a better
quality picture. The resolution is still only about 260-280
vertical lines. The main problems with 8mm are that you
can't replay 8mm tapes in a VHS machine (only watch or
re-record the signal), and the audio signal is embedded as
part of the video signal which means there is no way of
dubbling on a separate sound track on after the recording
has been made. 8mm is still a good choice when selecting a
camcorder because the cameras will be smaller and cheaper,
and the quality is marginally better than VHS or VHS-C.



SVHS

SVHS looks physically identical to VHS, but works in
completely different way. The colour and brightness signals
are separated and recorded separately on the tape. This
keeps noise effects such as "crosstalk" to a minimum and
gives a much better picture as a result. SVHS equipment is
the best consumer level available today (400-420 lines of
resolution), but is also very expensive. SVHS-C is a compact
version for use in camcorders.


Hi8

Hi8 is like 8mm, but in the same was as SVHS, separates the
luminance and chrominance information for a better quality
image. Hi8 equipment is expensive and hard to come by.






Animation Problems

Creating animations on the Amiga is easy, with packages like
Deluxe Paint, Imagine and Lightwave at your disposal.
However, replaying them at a decently frame rate can be a
problem.

First of all, if your animation is extremely detailed and in
hi-resolution, it will be very hard to get it to play back
smoothly. This is a limitation of the Amiga video hardware,
and it's a tought problem to get around.

Stick to lo-res screens if you can: HAM8 images still look
pretty good. Another good tip is to avoid having too much
movement on-screen at once. If using an image rendering
program, try to lock the camera in one place and one
direction. Having to constantly update a moving background
will slow down the animation drastically.

Having enough memory to put together a decent length of
animation is also a problem. There's 22Mb in this Amiga
4000, and it's still not enough at times! If you have a hard
drive, it's possible to get programs which will replay
animations directly from the disk. Speed can be a problem
here, so again keep colours, image size and movement to a
minimum.

If you have a spare Zorro slot and enough money, there are
several ways around this problem. First of all, a
single-frame advance video deck can tape your animation and
record it frame-by-frame to video tape. The Amiga displays
the image, instructs the video the record the frame and
then displays the next frame and so on. A deck like this is
expensive and assembling a length film frame-by-frame is a
time consuming process.

An alternative is to hand to problem over to electronics and
hardware image compression. There are at least two systems
for the Amiga which can capture and replay full-colour
images in real time. Both use the same technique, both take
slightly different approaches.

The key is JPEG -- the image compression scheme used by
programs such as Art Department and Pegger. Although rather
slow in software, JPEG is terrific for compressing detailed
pictures -- it can easily squash an image from 100K to 10K.
When the JPEG algorithm is converted to run on a single
chip, it because much faster and a good system can work in
real time. Incoming video is converted to JPEG and stored on
disk as individual files, outgoing video is replayed at 25
frames a second.

The DPS PAR card uses an IDE hard drive on a card along with
the JPEG hardware to achieve the speed necessary to replay
images at a sensible rate. The images can be any JPEG file,
and so you could render or draw all the images you want in
as many colours and with whatever movement you want, and
still be sure of a constant playback rate. The PAR card is
very expensive though, and a video capture card is another
£900. The VLAB Motion card works in a similar way, but
instead makes use of the Amiga's own hardware: although a
SCSI2 device is required for good results. The VLAB card
costs £1000, but comes complete with a video capture
feature. It's like having a digital video recorder: you can
record video, process it with a program such as Art
Department and then play it back.

The advantage that JPEG compression has over the more
popular MPEG system is that the chips required for MPEG
compression are still extremely expensive -- even though an
MPEG replay chip is only about £30.